The paper presents the results of investigation of self-assembled GeSi islands growth on Si (001) at 700 degrees C and the evolution of Ge islands parameters during annealing. The islands with the narrow (standerd deviation similar to 6%) lateral size and height distributions were grown. Dissolution of Si in islands was revealed from the Raman scattering and the X-ray diffraction measurements. Both the alloy composition and the elastic strain in the islands were determined. It was found that the content of Si in islands increased during annealing. This increase was shown to result in changes of the shape and sizes of islands.